The miniaturization, thinning or slimming, and pitch-reduction of semiconductor packages have rapidly been accelerated, in response to the recent requirements for the development of compact and light weight, and high quality electronic machinery and tools. In addition, the surface mounting technique has been a leading mainstream of the packaging method because this is quite favorable for realizing high density packaging of a wiring board or substrate. As the semiconductor packages and the methods for packaging the same have thus been advanced, there have been requested for the semiconductor-sealing material to satisfy the requirements for the improvement of functions thereof such as the quality, in particular, moldability, heat resistance, and flame-retardancy. For this reason, for instance, investigation has been made concerning incorporation of ceramic powder, in particular, amorphous spherical silica powder into epoxy resin in a high density. The problems arising when incorporating ceramic powder into a resin at a high density (or high content) are those that the viscosity of the resulting semiconductor-sealing material increases and that this in turn increases the rate of defectives to be formed during the molding and processing of the semiconductor devices such as the generation of unfilled portions, the occurrence of wire-flowing, wire-cutting and chip-shifting.
To solve the foregoing problems, the semiconductor-sealing materials have been improved from the viewpoint of resins on the one hand and from the viewpoint of the ceramic powder on the other hand.
As means for the improvement of the ceramic powder, there have been known, for instance, a method for increasing the Wardell to a level ranging from 0.7 to 1.0 (see Patent Document 1 specified below); a method in which the gradient of the straight line illustrating the particle size distribution expressed in terms of the Rosin-Rammler line diagram is set at a level of 0.6 to 0.95 to thus expand the particle size distribution (see Patent Document 2 specified below); and a method in which the ceramic powder is so designed that the particle size thereof has a multi-peak particle size distribution or that the particle size distribution thereof may have several peaks to thus bring the ceramic powder close to that having the closest packing structure (see Patent Document 3 specified below). However, these conventional methods have still been insufficient. More specifically, there has not yet been solved such a problem that when increasing the rate of incorporation of ceramic powder into a resin, the resulting semiconductor-sealing material causes an abrupt increase of the viscosity thereof.
Recently, electronic machinery and tools have widely been applied to automobiles and therefore, it has been requested for these electronic machinery and tools to satisfy the following requirements: they should have an improved flame-retardancy without using any flame retarder which may apply a high load to the environment; they should have an improved ability to withstand high temperature environmental conditions severer than that required for the household machinery and tools (heat resistance); and it should have an improved ability to withstand the cooling-heating cycles (thermal shocks). However, there has not yet been developed any such ceramic powder which can satisfy all of the foregoing requirements.    Patent Document 1: JP-A-3-066151;    Patent Document 2: JP-A-6-080863;    Patent Document 3: JP-A-8-003365